<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
	</head>
<style>
	body{
		background-color: red;
	}
.overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 9999;
}

.square-container {
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5); /* 遮挡面板背景色 */
    display: flex;
    justify-content: center;
    align-items: center;
}

.square {
    width: 200px;
    height: 200px;
    background-color: rgba(255, 255, 255, 0.5); /* 中间正方形透明背景色 */
    border: 2px solid #fff;
}
</style>
</head>
<body>

<div class="overlay">
    <div class="square-container">
        <div class="square"></div>
    </div>
</div>

</body>
</html>
